Recently, the case to install the EGR (Exhaust Gas Recirculation) cooler in vehicles is increasing in order to cut down NOx contained in exhaust gas emitted from a diesel engine, since social requests related to improvement of the natural environment is increasing. Furthermore, the necessity to install plural connected EGR coolers in one vehicle is also increasing in connection with request to improve performance of the EGR cooler.
FIG. 4 shows a prior art structure for connecting heat exchangers. At the structure for connecting heat exchangers, two EGR coolers 1, 2 are connected in series by welding each end of a U-bend pipe 5, respectively, to each body part 3, 4, which cooling fluid passes through, because of space problem in the engine room of the vehicle.
After the cooling water, which enters into the first EGR 1 cooler through an inlet pipe 6, enters into the second EGR cooler 2 through the U-bend pipe 5, it comes out of a outlet pipe 7. In the meantime, the cooling water exchanges heat between the exhaust gases passing through heat transfer pipes (not shown) installed in each body part 3, 4 and cools down the exhaust gases.
In addition, at the saltwater heat exchangers used in the nuclear power plant and the like, heat exchangers are connected by the U-bend pipe as the above case (See Japanese Unexamined Utility Model Application No. 56-89590).
However, in the above-mentioned prior structure for connecting heat exchangers, there are problems that it is difficult to form the U-bend pipe and to weld it to the each body part. Also, costs for parts and labor are expensive, because it is necessary to use the U-bend pipes, which bend radius is small, to connect the heat exchangers.
Furthermore, there is a problem that it is difficult to install the U-bend pipe in the small space, such as the engine room of the vehicle, because a little space is provided to install the U-bend pipe.
In addition, there is a problem that it is difficult to improve the efficiency because fluid resistance and power for transferring the fluid become larger.
In order to overcome the above problems, the object of the present invention is to provide a structure for connecting heat exchangers to be able to reduce the cost and space for installation and to improve the efficiency.